A knowledge of the spacial distribution of light in tissue is of critical importance for many applications in photobiology and laser medicine. Photodynamic therapy (PDT) is a cancer treatment procedure in which a patient is injected with a photosensitizing dye. The dye injection is performed several hours to several days before photodynamic therapy is performed. This time period allows the photosensitive dye to localize and concentrate in abnormal target tissues such as cancerous tumor masses. Photodynamic therapy involves irradiation of the abnormal target tissue cells with laser light at an appropriate wavelength. This irradiation results in destruction of the targeted cells.
Under ideal conditions the use of the photosensitive dye causes the targeted tissue to be more susceptible to more susceptible to treatment irradiation. However, normal or non-targeted tissue exposed to the treatment irradiation, i.e., healthy tissue immediately surrounding a targeted tumor mass, will be destroyed if its exposure to the phototherapy irradiation exceeds a threshold value. On the other hand, if the targeted tissue does not receive sufficient phototherapy irradiation, it will not be destroyed and the therapy will not be successful. Accordingly, safe and effective application of photodynamic therapy requires accurate and adequate light delivery together with careful monitoring of the phototherapy irradiation.
The accurate measurement of light levels in a turbid media, such as cellular tissue, requires the use of a dosimetry probe that has an isotropic (angular) response. There are currently two types of isotropic dosimetry probes used in photodynamic therapy procedures.
Fiber optic dosimeter probes with highly scattering, spherical tips have been developed which exhibit approximately isotropic responses within a field that extends from the forward direction of the probe tip to about 150.degree. from the forward direction. Such spherical-tipped probe designs provide a much weaker response to irradiation beyond about 150.degree. from the forward direction. One disadvantage associated with spherical-tipped fiber optic dosimeter probes is that they necessarily have significantly large diameters. Typically, the sphere portions are about 800 .mu.m in diameter and the optical fiber cores are about 400 .mu.m in diameter. Spherical-tipped fiber optic dosimeter probes are also extremely fragile due to their size and geometry.
Fluorescent-tipped fiber optic dosimeter probes are also known to demonstrate isotropic responses. In addition, such fluorescent-tipped fiber optic dosimeter probes offer the advantage of generally having much smaller dimensions and being more rugged than spherical-tipped fiber optic dosimeter probe designs. Because of their small size, fluorescent-tipped fiber optic dosimeter probes can be inserted through hypodermic needles. Although they offer a size advantage, fluorescent-tipped fiber optic dosimeters exhibit a lower responsivity (defined as fluorescent light power per incident local fluency rate at the dosimeter probe tip) than spherical-tipped fiber optic dosimeter probes. Nevertheless, their use is often preferred in photodynamic treatment procedures in which size and strength are important considerations.
The present invention provides fiber optic dosimetry probes which have isotropic responsivities over a wide wavelength range to produce a narrow response emission and which overcome many of the disadvantages associated with prior art fiber optical dosimetry probes.